A bet that must be posted by the winner of a scoop pot above a certain size in a seven-card stud high-low game. The bet signifies a full bet (i.e., a blind raise), rather than just a call of the original forced bet (i.e., the bring-in).
Any player who acts before the action button can only call the bring-in. The holder of the action button essentially raises blind, and then, when it gets back to those who have only so far called the opening bet, they can either call or raise.
"Action buttons" can also refer to clickable buttons or boxes in online poker able to be selected in advance of a player's turn.